Heretofore, fluoroplastics resistant to chemical attacks have been used in the application where chemical resistance is required. Utilizing their inherent low refractive index, fluoroplastics are also employed in the antireflection application as in displays. However, when the fluoroplastics are used as rubber or coating compositions, their molecular structure makes it difficult to form hard protective coatings having mar resistance.
Recently, hydrolyzable silane compounds having perfluoroalkyl groups were developed. To take advantage of their favorable characteristics, a variety of coating compositions comprising hydrolyzable silane compounds have been developed for imparting water repellency, oil repellency, anti-staining and anti-reflection. However, since perfluoroalkyl groups contributing to these favorable characteristics are bulky and inert, the cured coatings have a low crosslinked density. As a result, the cured coatings are fairly hard as compared with fluoroplastics, but still lack mar resistance.
Several systems were developed for enhanced mar resistance. For example, JP-A 2002-53805 describes co-hydrolysis of a perfluoroalkyl group-containing silane and a silane compound such as a tetraalkoxysilane; JP-B 6-29332 describes a system comprising a perfluoroalkyl group-containing silane, a disilane compound having perfluoroalkylene as a spacer, and a tetraalkoxysilane; and Japanese Patent No. 2,629,813 describes a system comprising a disilane compound having perfluoroalkylene as a spacer and an epoxy-functional silane. These systems achieve fairly satisfactory levels of desired properties such as anti-staining, mar resistance, adhesion and antireflection. However, because of a reduced fluorine content, they lack chemical resistance to such chemicals as household detergents. Especially the lack of alkali resistance is outstanding as the weak point of polysiloxane systems. This is problematic on practical use.
There are available no coating compositions that satisfy both mar resistance sufficient to protect transparent substrates and practically necessary chemical resistance to household detergents used in cleaning. There are available no coating compositions that possess multiple functions of antireflection, anti-staining, water repellency and the like as well.